Cholesterol is the principal animal sterol. It occurs in all tissues of the animal body. It is synthesized by all tissues in the body but is also taken in as part of fatty foods. Its concentration in the blood is from 150 to 250 mg per 100 ml and depends upon intake in the food and increases with age. Its main function in the blood is the transport of fats and fatty acids to and from the liver.
It is a common belief that there is a correlation between high levels of cholesterol in the blood and atherosclerosis, a disease of large arteries, characterized by plaque-like intimal deposits which contain neutral fat, cholesterol, and sometimes blood. This condition leads to gradual narrowing of the arterial lumen, ulceration of the intima. The development of a thrombus around the plaques can cause coronary disease, cerebral thrombosis (stroke), and peripheral arterial narrowing with gangrene.
Arteriosclerosis is the end result of atheromatosis; i.e., hardening of the arteries. Restriction of cholesterol intake in the food has been recommended to lower the blood cholesterol levels. This has not been generally effective because the synthesis of cholesterol in the body appears to supply the body's needs for cholesterol and can be only in part controlled by intake. On the other hand, the need for cholesterol is enhanced by increasing the fat in the diet, such as butter and animal fat, which then require higher amounts of cholesterol for their metabolism and transport in the body.
Several drugs have been introduced in attempts to control the amount of cholesterol in the blood, known as hypocholesterolemic agents. Such drugs have clinical utility for patients who do not respond to dietary treatment. The hypocholesterolemic effect of such drugs may result from interference with synthesis of cholesterol; from inhibition of its absorption from the digestive tract; from a hastening of its metabolic degradation or some as yet unknown type of action.